This manga is called a seinen, but the story is full of shonen clichés... For example, the phrase "I must protect everything I love, I must protect everything that is important to me", if I had a peny for every time the main character said this phrase in every shonen I watched and read. , now I would be even richer than Elon Musk. Then, in order to achieve this phrase, there is the you need to get stronger by training, especially against a strong enemy, learning to use your power or learning a new technique, and the enemy you fight against later joins your team as your friend... etc. Shonen clichés like these were in this manga, so it would be more accurate to call this manga a battle shonen with excessive blood and gore scenes.
The story of the manga was not that original at all. Basicly, Human-looking monsters, who try to survive secretly in society, are a threat to humans and because of that they are hated and hunted. There were so many characters in the manga, I can't remember the names of many of the characters. After a certain point, I wasn't sure at first whether the mangaka added a new ghoul investigator character to the manga or we went back to and focused on an already excisting ghoul investigator character who was mostly in the background so far. Of course, this confusion went away when I realized that when the mangaka added a new ghoul investigator character to the story, he showed the ghoul investigator character's name, rank, Quinque (a special weapon used by ghoul investigator while hunting ghouls) technique and the name of the ghoul investigator character's Quinque.
The manga made me read without getting bored due to its abundance of action, otherwise I would not have been able to finish reading all the 144 chapters. I like shonen anyway, I just expected more from a manga that is considered a seinen.